This invention relates to the generation and display of computed images, and more specifically, to the visual presentation of an airfield runway and associated visual cues necessary for accurate aircraft flight simulation. While the invention is described in particular detail with respect to such visual simulation use, those skilled in the art will recognize the wider applicability of our invention to other applicational forms of computer generated display images.
The prior art exhibits a number of examples of devices useful in providing CRT displays of desired images. The invention described hereinafter is particularly concerned with the use of CRT displays in aircraft flight simulators. Commonly, modern simulators are exact mock-ups of the particular aircraft for which training is being provided. That is to say, the flight deck of a particular aircraft is recreated so that flight crews can fly the simulator prior to flying the actual aircraft. It is conventional to provide sound, motion, and visual sensory perception to the flight crew during such simulated flight. Modern simulators provide physical sensations that closely approximate those experienced in actual flight.
One of the more common simulation experiences for which training is provided is landing and takeoff of the aircraft. Commonly, the pilot of the simulator is provided with CRT (Cathode Ray Tube) displays which correspond to the window view of the pilot. That is, the windows of the aircraft are replaced in the simulator by CRT displays. A computer generated graphic scene, or a closed circuit television system using a scale model of the scene to be displayed is utilized to control the CRT display and to provide the image desired. Presently, two computer generated graphic methods commonly are employed to generate two and three dimensional objects on a conventional CRT display. One method places the beam at a particular location on the face of the display, and moves the beam from its start position to a designated end point, thereafter redesignating the beam to a new starting point. The second method requires the element by element computation of the intersection of the scene viewed through the aircraft window with the raster background. In either case, complex circuitry is required to generate the required control voltages with sufficient speed and precision when a number of scene components are displayed.
The invention disclosed hereinafter provides a real time window image to an observer by determining the control points of a desired outline for a given shape. These control points are converted to X-Y coordinates corresponding to the CRT display. Left edge and right edge vectors are generated which connect an initial point to successive ones of the outline calculated points. The vectors consist of line segments, placed end-to-end, defined by line segment start point and the slope to the next line segment start point. The shape is constructed by sweeping the CRT beam in the X coordinate direction, and comparing the instantaneous X beam position with the left edge and right edge vectors. Upon comparison, beam intensity is blanked, the Y coordinate of the beam incremented, the beam direction reversed, the beam intensity again unblanked, and new vector edge values are generated. A wide variety of image shapes can be presented utilizing this technique.
The particular embodiment disclosed also provides means for varying the intensity of the display for additional display realism. In general, prior art devices also have required complex circuits to obtain intensity variation of a generated scene. As will be appreciated by those skilled in the art, it is desirable, in simulator design, to provide a depth cue to the pilot in addition to the impression of depth provided by conventional perspective. The invention disclosed accomplishes intensity variation by generating a shading function in real time which is controlled by predetermined intensity coefficients at the corners of the display window and by the instantaneous X-Y position of the beam of the CRT.
One of the objects of this invention is to provide a more economical device for generating deflection voltages for a CRT display.
Another object of this invention is to provide an electronically less complex device for generating control voltages for a CRT display.
Another object of this invention is to provide a CRT display having increased realism over known prior art devices.
Yet another object of this invention is to provide a CRT display in which the beam is swept in the X coordinate direction and reversed in a blanked-out area of the screen.
Another object of this invention is to provide an improved method and device for generating a shading function for a CRT image.
Other objects will be apparent to those skilled in the art in light of the following description and accompanying drawings.